As electronic devices increasingly become portable, advances must be made to guarantee the safety and reliability of portable energy storage systems. The industry emphasis on portability and long use times has resulted in large increases in energy storage capacity and or power output rates, quantities that correspond to the magnitude of potential hazards if a cell should fail or be abused. Therefore it is of mounting importance to have quality control mechanisms for assembly and handling of the energy storage device.
Numerous different battery systems have been proposed for use in portable applications over the years. Among the earliest were primary (i.e., non-rechargeable) alkaline cells. Early rechargeable battery systems included lead acid, and nickel cadmium (NiCad), each of which has enjoyed considerable success in the market place. Lead acid batteries are preferred for applications in which ruggedness and durability are required and hence have been the choice of automotive and heavy industrial settings. Conversely, NiCad batteries have been preferred for smaller portable applications. More recently, nickel metal hydride systems (NiMH) have found increasing acceptance for both large and small applications. In order to achieve high current rates, e.g. for digital pulse electronics applications, a new class of cells is also now emerging, generally referred to as electrochemical capacitors (ECC).
Higher voltage cell chemistries are evolving and finding a place in cell markets, the most prominent current example being lithium ion cells; these are for the most part non-aqueous. However, aqueous based systems such as lead acid, Nicad, NiMH, ECC, and primary alkaline cells continue to be popular among consumers. Cell manufacturers continue to look for ways to improve the quality of these aqueous based cells as well as more advanced cells, and to detect defective cells either during manufacturing or at later points. Leaks often correlate with a variety of internal cell malfunctions, including transient short circuits in cells, high self-discharge, corrosion of tabs and current collectors, failure to pass current, and in addition electrolyte frequently damage the electrical devices for which they were intended to provide power. Cells that have suffered substantial leaks often are coated with a powdery residue, comprised of base, acid, and or salt that had been dissolved in the leaked electrolyte solution. However, such deposits may also result from the leak of a neighboring cell. For many purposes visual observation of residues is considered a crude, time consuming, and somewhat unreliable test, and one would prefer to have a method that would determine immediately which, if any, cells in a lot had leaked.
Accordingly, there exists a need for improved means of indicating electrolyte leaks.